This invention relates to a catalyst component for use in the polymerization of .alpha.-olefins and to a process for the polymerization of .alpha.-olefins using the same, and more particularly, it is concerned with a supported titanium catalyst component prepared by an improved process and with a process for producing a stereoregular homopolymer or copolymer of .alpha.-olefins using a catalyst system comprising the supported titanium catalyst component and an organo aluminum catalyst component.
For the stereoregular polymerization of .alpha.-olefins, it has hitherto been carried out to use a catalyst system comprising solid TiCl.sub.3, obtained by reducing TiCl.sub.4 by various methods, and an organo aluminum compound as cocatalyst. However, this method has many disadvantages on a commercial scale in that both the polymerization activity and stereoregularity of commercially available catalyst systems are low and steps for polymer deashing and for removing amorphous polymers are required. In order to overcome these disadvantages, there have been proposed processes for the polymerization of .alpha.-olefins by the use of catalyst systems comprising, by way of example, titanium catalytic components obtained by treating solids, obtained by reducing TiCl.sub.4 with organo aluminum compounds, with complexing agents and then with TiCl.sub.4 (U.S. Pat. No. 4,210,738 of Hermans et al, issued July 1, 1980); or by treating the solids with complexing agents and hexachloroethane (U.S. Pat. No. 4,182,691 of Ueno et al, issued Jan. 8, 1980). In these examples, as far as solid TiCl.sub.3 is used, however, only a part of the titanium can be utilized as an active catalyst and, consequently, there is not obtained such a high catalytic efficiency as to omit the polymer deashing step.
As a desirable method for raising the polymerization activity per unit titanium, on the other hand, it has been known to disperse and support titanium compounds on other solids. Actually, in the production of polyethylene by middle or low pressure process, a high catalytic efficiency can be achieved by the use of a catalyst system comprising a titanium catalyst component (titanium compounds on various supports) and an organo aluminum compound component. A polymeric product of good quality can be produced on a commercial scale without a polymer deashing step. However, in the polymerization of higher .alpha.-olefins, e.g., propylene, a high polymerization activity as well as a high stereoregularity are required, resulting in a more difficult problem than in the case of producing polyethylene by middle or low pressure process.
Of late, various improved methods have been proposed as to the stereoregular polymerization of .alpha.-olefins using a catalyst system comprising a supported titanium catalyst component and an organo aluminum catalyst component. Typical methods thereof are as follows:
1. A method comprising using a catalyst system comprising a solid supported titanium catalyst component obtained by cogrinding anhydrous MgCl.sub.2, TiCl.sub.4 and an electron donor, e.g., an organic acid ester, or a complex of TiCl.sub.4 and such electron donor, and an organo aluminum catalyst component comprising an aluminum compound and electron donor (U.S. Pat. Nos. 4,107,413, issued Aug. 15, 1978; 4,107,414, issued Aug. 15, 1978; 4,156,063, issued May 22, 1979; 4,187,196, issued Feb. 6, 1980; and 4,226,963, issued Oct. 7, 1980, all of Giannini et al);
2. A method comprising using a catalyst system comprising a supported titanium catalyst component, obtained by ball milling anhydrous MgCl.sub.2 and an electron donor (and a silicon compound) and contacting with TiCl.sub.4 with heating to support the titanium compound, with catalyst component of an organo aluminum compound and electron donor (British Pat. No. 1,492,618, published Nov. 23, 1977, of Mitsui Petrochemical Industries Ltd. and U.S. Pat. No. 4,226,741, issued Oct. 7, 1980 of Luciani et al).
In addition to these methods, there has also been proposed, by way of further example, a method comprising using a catalyst system comprising a supported titanium catalyst component, prepared by treating with a solution of an organic acid ester, a titanium-containing solid obtained by heat treating MgCl.sub.2.mROH in TiCl.sub.4, and an organo aluminum compound component (Japanese Patent Public Disclosure No. 57789/1976), but this method is insufficient in eliminating polymer deashing.
The inventors have made various studies on the supported titanium catalysts used in the above-described prior art methods and, consequently, have found that these methods have various disadvantages. That is to say, the method (1) is advantageous in that the titanium-containing compound component can effectively be utilized and handling thereof is easy, but produces inadequate results in overall polymerization activity and stereoregularity for omitting the steps of polymer deashing and removing amorphous polymer products. The surface area of the supported titanium catalyst component thus produced is small, as described in U.S. Pat. Nos. 4,107,413, issued Aug. 15, 1978; 4,107,414, issued Aug. 15, 1978; 4,156,063, issued May 22, 1979; 4,187,196, issued Feb. 6, 1980; and 4,226,963, issued Oct. 7, 1980, all of Giannini et al.
In the method (2), a large excess of TiCl.sub.4 is used for supporting, so steps for recovering and purifying the same are required. It is difficult to remove completely free TiCl.sub.4 adhered to the support after being supported. If this removal is not sufficiently effected, the polymerization activity and stereoregularity are unfavorably affected and in order to prevent this, it is necessary to provide a multistage washing step, which is disadvantageous commercially.
The inventors have continually made efforts to solve the problems on these supported titanium components, and have thus reached the present invention.